New Entry Points

• add pkg.exports entry-points for CJS + ESM
• add namespace entry-points
• legacy Node now works via pkg.main
• refactor tests to use namespace imports directly
• refactor tests with better variable names and to fix spelling mistakes
• refactor types
• update README.md
• add 'Experimental' notice for Node users to README.md
• update the debug config (use Node 13.7)
• add CHANGELOG.md
• add CommonJS compatibility test